Your MBP may still be in good working condition by then if you take care of it. But there will likely be enough advances, upgrades and improvements by then that you will want to upgrade to a newer model. When a new OS comes out, it adds functionality, and some older programs may no longer work. And new programs that come out may not run on older hardware.

I'm hoping to get years more than that out of my macbook; I mean it'll be very acceptable for writing up essays for many years. When I switched to Mac one of the reasons was to get out of this hardware race where you just throw money into the whirlpool of getting the newest just so you can run the latest software &c. If you look at the PowerPC board you'll see people using Tiger- and not just for surfing/word-processing).

(I was writing up essays for uni on Windows 3.1, and that was six years ago lol!)

MacRumors attracts a broad audience
of both consumers and professionals interested in
the latest technologies and products. We also boast an active community focused on
purchasing decisions and technical aspects of the iPhone, iPod, iPad, and Mac platforms.